The main components of a waterjet propulsion apparatus are an intake section, a pump, and a nozzle. Water enters the unit through the intake section, which scoops water into the apparatus and directs it in the aft direction. The pump includes a rotor, also referred to as an impeller, and a stator located downstream thereof, both of which are located within a water conduit or flowpath. The rotor is turned on a shaft that is driven by the prime mover of the vehicle. The rotor adds energy to the water, which then has a higher velocity and pressure. The swirl induced by the rotor is for the most part removed by the stator, which does not rotate. At the outlet end of the conduit, downstream of the stator, is located a funnel-shaped nozzle, which reduces the cross-sectional area of the flowing stream and thereby increases the thrust. In some embodiments the stator and the nozzle are an integrated unit. The thrust produced by the pump propels a marine vehicle.
The rotor is supported on bearings which are protected by a lip seal assembly to prevent high-pressure water from leaking into a bearing cavity of the apparatus. Water leakage into this area may result in bearing corrosion and possible bearing failure. Typically the lip seal assembly is subject to high static pressure at the gap between the rotor exit and stator inlet. This high pressure may result in seepage of water into the bearing cavity due to heavy wear on the lip seal assembly elements, and consequent corrosion of the bearing assembly in the bearing cavity.
Accordingly, it is desirable to provide for an improved waterjet propulsion apparatus that includes a reduction in excessive lip seal wear and the possibility of water leakage into the bearing cavity due to high pressure upstream of the lip seal assembly. In addition, it is desirable to extend the life of the component elements of the lip seal assembly. Finally, it is desired to provide a system for preventing corrosion to the bearing assembly in a waterjet propulsion apparatus that is less costly as compared to the alternative of replacing a damaged lip seal assembly and a bearing assembly with new ones. The present invention addresses one or more of these needs.